You sound concerned about the exposure of the food to heat, not freezing.

MREs will work fine. So will most canned foods. So pack a few things that you like to eat that don't require cooking away in the trunk of your car and feel good about it.

I would think packing the food in a small/med. cooler could serve two purposed, 1)provide a storage container and 2)prevent any rapid temp. swings up or down during storage.